ANISOTROPY AND TRANSVERSE ISOTROPY*

A number of authors in the exploration literature have written about anisotropy, but have restricted their discussions to wave propagation through rock having transverse isotropy with a vertical symmetry axis. This note shows that there are fundamental differences between transverse isotropy when the symmetry axis is vertical (normal to the free surface) and more general anisotropy with an azimuthal variation of properties. These differences are important now that effective azimuthal shear-wave anisotropy resulting from aligned cracks and pores is becoming recognized as a significant property of crustal rocks.     

SEISMIC CLASSIFICATION OF ROCK MASS QUALITIES*

Correlations between longitudinal velocities and rock mechanic parameters such as fracture frequencies and “Rock Quality Designation” (RQD) values have been studied, based upon velocity data from various rock types and different geographical locations. The dispersion of values at different sites studied is on average ± 0.8 cracks per meter and for the RQD values ± 3.5%. Within sites the dispersion of individual values relative to the average for the site is ± 1.0 – 2.0 cracks per meter and ± 2 – 6% for the RQD values. The deviations are rather moderate, especially when considering the variation of rock type involved in the studies: amphibolite, granite, gneiss, meta-anorthosite, pegmatite, porphyry, quartzite, and mylonite. The studies thus confirmed earlier assumptions that there is a strong correlation between longitudinal velocity and fracturing and that the velocities can be used to give rather accurate predictions of the quality of rock masses for construction purposes. The accuracy of the predictions increases if the velocity level of the more competent rock is taken into account. The correlation between velocity and fracturing is related to jointed but unweathered igneous and metamorphic rock and cannot be applied without introducing serious errors to a site where the rocks present a higher degree of alteration and weathering. Comparisons between rock permeability and longitudinal velocity proved that a more reliable general correlation is not likely to be found. By comparing the elastic moduli E_dyn, μ, and k with ø, V_p/V₈, and k/μ, indications have been obtained where the optimum rock conditions for a certain site are to be encountered. This has been verified by a similar comparison where the elastic moduli have been replaced by fracturing values. The value of the longitudinal velocity as a means to evaluate rock quality increases if the position of the velocity in the range of the Poisson's ratio has been established. The average relationships between longitudinal velocities and the corresponding elastic moduli proved to be: The values from each site differ from the average values with about ± 2 GPa for E_dyn and about ± 1 GPa for μ and k. It was confirmed that in igneous and metamorphic rocks longitudinal velocities ≤ 4000 m/s generally indicate rock masses where heavier tunnel support will be needed. This velocity limit corresponds to an average fracture frequency of about 10 cracks per meter and a RQD value of about 65 %. The prediction of the tunnel reinforcements needed at a particular site will, however, be improved if the general velocity level of the more competent rock is considered.     

THE CLASSIFICATION OF PHYSICO-GEOLOGICAL MODELS OF MINERAL DEPOSITS*

We describe the concept of physico-geological models (PGMs) in geophysical exploration. They represent a “general model”, a spatial combination of a set of particular models (disturbing bodies). The modeling is called complete, incomplete or approximate, depending on the degree of characterization of the PGM by parameters such as dimension, shape and petrophysical property. Each of the three modeling types can be realized as a conceptual, and analytical, or a material PGM. Both deterministic and stochastic PGMs exist; deterministic models are mainly used to investigate the possibilities of a geophysical method, while stochastic models serve to substantiate complex geophysical interpretations. Depending on the geological problem, PGMs are subdivided into multi-alternative models (geological mapping, prediction, general prospecting) and double alternative models (specialized prospecting). An exploration-oriented classification of the PGMs of mineral deposits is discussed. According to this classification the variety of known genetic deposit types is reduced to a limited number of generalized PGM types. The development of typical PGMs is illustrated with examples of magnetitic deposits of Siberia.     

SOME EXPERIMENTS ON TRANSVERSE WAVES*

In-situ seismic measurements on shear waves propagation both in soft formations (clays) and in hard formations (calcareous rocks), using several field techniques did not result in clear S arrivals. Particular digital approaches were then used, based on spectral analysis of records, for the selection of the seismic events and the calculation of their propagation velocity. The actual application of these numerical procedures are described and to some records obtained using the “crosshole” field technique show that the suggested procedures are a substantial contribution to the identification of transverse waves.     

A SYSTEMATIC APPROACH FOR EVALUATING AIRBORNE ELECTROMAGNETIC SYSTEMS*

Airborne electromagnetic methods have been in use for more than 30 years. The selection of the most effective airborne system for a given geological/geographical environment is difficult since there are only a limited number of theoretical comparisons and very few comparative field evaluations of the systems. Shell Canada Ltd carried out a field evaluation using several systems to provide such a comparison. For this evaluation five different airborne systems were flown over 22 conductive features. Some lines were flown at various directions to strike, some at various elevations, and some with different line spacings. The airborne systems were then evaluated target by target for navigational control, line-to-line correlation, resolution, lateral coverage, signal strength, noise etc. The paper examines the philosophy behind our field evaluation and outlines steps required for setting up this comparison. Pitfalls are discussed as well as examples which illustrate the methodology. Two field examples are given from the Bathrust mining camp in New Brunswick and the Timmins Clay belt in northern Ontario (both in Canada). Some general conclusions which help our understanding of present day airborne electromagnetic systems are discussed at the end of the paper.     

地震检波器的横向灵敏度特性

地震检波器受到地面横向运动激励时的输入输出关系定义为检波器的横向灵敏度特性.本文对检波器线圈受到横向激励时产生的轴向振动进行了分析.可以看到,当悬挂线圈的弹簧片悬丝发生动力失稳时,检波器的横向灵敏度突然增大;在线圈横向振幅很小的情况下,失稳频率接近悬丝的横向固有频率.利用谱分析技术可以准确地从检波器噪声中检测出检波器的横向灵敏度和失稳频率,即检波器假频.     

地震检波器的横向灵敏度特性

地震检波器受到地面横向运动激励时的输入输出关系定义为检波器的横向灵敏度特性.本文对检波器线圈受到横向激励时产生的轴向振动进行了分析.可以看到,当悬挂线圈的弹簧片悬丝发生动力失稳时,检波器的横向灵敏度突然增大;在线圈横向振幅很小的情况下,失稳频率接近悬丝的横向固有频率.利用谱分析技术可以准确地从检波器噪声中检测出检波器的横向灵敏度和失稳频率,即检波器假频.     

考虑流-固耦合梁式矩形渡槽横向地震响应研究

根据豪斯纳尔（Housner）理论, 建立了考虑槽内水体与渡槽槽身流-固耦合的横向地震响应计算模型,分析了槽身断面深宽比变化对渡槽结构抗震的影响,并对某大型渡槽进行了多工况地震时程响应计算. 结果表明,在地震波作用下,渡槽槽内大质量水体对渡槽的横向地震响应有较大的影响, 但水体的晃荡作用有明显的TLD效应. 若将水体视为刚体, 质量全部附加到槽体上,将严重地夸大水的地震惯性力作用,且在渡槽槽身断面选择时应考虑深宽比对墩身地震响应的影响, 以减小地震力.      

低速太阳风的分类

对1970-1980年1AU附近太阳风的观测资料所进行的分析表明,60％的冕旒相关流和40％的CME相关云的流速都不大于350km/s;80％的流速不大于350km/s的低速风起源于冕旒,且除冕旒和CMEs外,看来还存在别的低速风日冕源区.有关冷风的分析表明,近80％的冷风的流速不大于350km/s,80％的冷风起源于冕旒;也有一小部分冷风既非起源于冕旒,也不起源于CMEs.低速风的11年变化显示,在太阳活动各位相,冕旒总是低速风的主要日冕源区.但是,极大位相时的冕旒宽度很可能大于极小和下降位相.     

低速太阳风的分类

对1970—1980年1AU附近太阳风的观测资料所进行的分析表明,60％的冕旒相关流和40％的CME相关云的流速都不大于350km/s;80％的流速不大于350km/s的低速风起源于冕旒,且除冕旒和CMEs外,看来还存在别的低速风日冕源区.有关冷风的分析表明,近80％的冷风的流速不大于350km/s,80％的冷风起源于冕旒;也有一小部分冷风既非起源于冕旒,也不起源于CMEs.低速风的11年变化显示,在太阳活动各位相,冕旒总是低速风的主要日冕源区.但是,极大位相时的冕旒宽度很可能大于极小和下降位相.     

STATE OF MAGNETOSPHERE AND MICROPULSATION CLASSIFICATION

Geomagnetic pulsations are usually classified into pc1-pc5 and pi1-pi2 according to the wave form and the period range. In this paper authors′attempt is to purpose a new classification with reference to the state of magnetosphere and the mechanism of excitation.     

水平形变资料系统误差分析方法

高精度物理测距仪的发展,为我们获取地壳水平运动微量信息提供了可能,但观测资料中存在着干扰因素的严重影响,其量级有时甚至比偶然观测误差大几倍。     

震级一频度曲线呈系统性起伏的可能性及影响

自从对全球而言的古登堡—里克特关系:lgN(m)=a-bm,被推广应用于各具体的地震区带的地震活动性研究以来,有成功的例子,有艰难但仍获解释的例子,也有谨慎但论据充足的反例。其实,对于第二种情况而言,也未必就不是反例。本文拟从数学反证的角度,证明对于具体的地震区带而言,其震级-频度曲线呈现系统性起伏是可能的。考虑到震级-频度曲线在短临预报和中长期预报中应用广泛,本文还简要评述了如果忽视其系统性起伏可能导致的后果。     

辽宁省流动数字测震台网系统化集成

针对辽宁省现行的流动数字测震台网设备及各个部件比较离散、部分体积较大等不足之处进行高度的系统化集成,使整个应急流动数字测震台网系统更加完善、设备安装及运输更加便捷、缩短设备架设的时间、降低故障点,从而使之能够更好地为地震监测工作服务。     

关于地震烈度衰减模型的系统偏差

本文讨论在地震危险性分析中目前使用广泛的地震烈度衰减模型,即Cornell建立的点源模型和洪华生(A.H-S.Ang)等建立的断层-破裂模型。与实际烈度资料的比较表明,在等震线狭长的区域,点源模型有系统偏差,通常这种偏差不算严重。为了克服上述偏差,断层-破裂模型引进了破裂长度的概念,但其衰减与实际资料出入较大。与实际地震等震线的比较和计算表明,对大地震沿断层或等震线长轴方向,断层破裂模型总是高估高烈度区而低估低烈度区。此外,本文分析了断层破裂模型产生系统偏差的原因,讨论了点椭圆模型的合理性,并用地震危险性分析实例做了说明。     

地震灾害的分类和分级方法研究

利用我国大陆地区1954——2005年成灾地震事件的数据和资料,运用多元统计分析方法,研究和分析了地震灾害的分类和分级问题,找出了地震灾害的3个基本结构,提出了主成分提取-最大正交旋转-因子分析（FAPE）分类模型和欧氏平方距离-离差平方和法-系统聚类（HCWS）分级模型. 运用该模型将地震灾害分为8种类型和5个等级,比较合理地解释了已有地震灾害现象.     

设定地震的分类及其确定方法

讨论了震害预测中的设定地震,将其分为检验型设定地震、预测型设定地震和重现型设定地震,并论述了３种设定地震的确定原则和方法．作者还进一步论述了３种设定地震在不同震害预测方法中的应用     

自然灾害与地球系统管理的科学思考

通过大量实际资料展现了目前我国生态环境的恶化状况及泥石流、崩塌、滑坡、地面沉降、诱发地震等地质、地震灾害的严重性;提出地球系统管理符合人类社会发展的要求,只有处理好各种人地关系,维护生态平衡,才能推进社会的可持续发展。     

利用对称四极横向剖面法探测走滑断层的应用

从走滑断层难以探测的实际出发,讨论了其物性特征;通过对低阻板模型的物理模拟、数值模拟以及对实地观测资料的分析,研究了对称四极纵、横向剖面法视电阻率曲线的变化特征和差异. 结果表明,横向剖面法相对纵向剖面法异常幅度明显增加,可对地震活动断层进行更为有效的探测和定位. 这一研究为走滑断层探测提供了新的思路. 同时,利用对称四极横向剖面法可以解决走滑断层难以探测这一技术难题.      

中国前震旦纪地壳构造运动旋回的划分

本文对我国三大断块(区)的前寒武纪地层的发育、建造类型、不整合及部分同位素年龄值进行了对比,划分出五个地壳构造运动旋回,即桑干旋回(2500—2600百万年前),五台旋回(2000百万年前),中岳旋回(1700百万年前),“阴山旋回”(约1200—1300百万年前)和晋宁旋回(1050—900百万年前)。指出在前震旦纪变质岩系中的不整合具有多次地壳构造运动的集合的性质,相当显生宙的一个构造旋回。同时指出晋宁运动具有明显的穿时性,与板块构造理论相符